feat: support private property definitions

[cdc-as81]

Summary

• Add private = true support to define_property! and
  define_derived_property!.
• Apply private visibility consistently across tuple structs, named-field
  structs, optional-value structs, and enums.
• Preserve public visibility as the default, including fields on public derived
  properties.
• Add targeted diagnostics for private = false and incorrectly ordered
  private options.
• Document the new option and add privacy, compatibility, and diagnostic tests.

implements #1032

[github-actions]

Benchmark Results

Hyperfine

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
large_sir::baseline	2.0 ± 0.1	1.9	2.2	1.00
large_sir::baseline_households	2.0 ± 0.0	2.0	2.1	1.01 ± 0.03
large_sir::entities	3.7 ± 0.1	3.6	3.9	1.84 ± 0.06
large_sir::households	3.7 ± 0.2	3.5	4.0	1.86 ± 0.10

Criterion

Regressions (slower)

Group	Bench	Param	Change	CI Lower	CI Upper
sampling	sampling_single_known_length_entities		33.302%	30.441%	36.320%
sampling	count_and_sampling_single_known_length_entities		22.737%	21.090%	23.940%
counts	multi_property_unindexed_entities		13.790%	11.105%	16.527%
counts	multi_property_indexed_entities		6.721%	5.591%	8.027%
sample_entity	sample_entity_single_property_indexed	1000	2.426%	2.007%	2.815%
sampling	sampling_multiple_unindexed_entities		1.934%	1.568%	2.283%

Improvements (faster)

Group	Bench	Param	Change	CI Lower	CI Upper
sample_entity	sample_entity_whole_population	1000	-9.814%	-11.190%	-8.365%
indexing	query_people_single_indexed_property_entities		-9.510%	-9.670%	-9.342%
sample_entity	sample_entity_whole_population	100000	-9.005%	-10.582%	-7.379%
sample_entity	sample_entity_whole_population	10000	-7.699%	-8.888%	-6.515%
counts	reindex_after_adding_more_entities		-6.431%	-6.702%	-6.166%
counts	concrete_plus_derived_unindexed_entities		-6.207%	-8.164%	-4.430%
examples	example-births-deaths		-3.130%	-3.302%	-2.973%
examples	example-basic-infection		-3.062%	-3.675%	-2.403%
indexing	query_people_multiple_individually_indexed_properties_entities		-2.923%	-3.154%	-2.697%
indexing	query_people_count_single_indexed_property_entities		-2.355%	-3.129%	-1.614%
sample_entity	sample_entity_single_property_indexed	100000	-2.309%	-3.042%	-1.529%
indexing	query_people_count_multiple_individually_indexed_properties_enti		-2.068%	-2.214%	-1.909%
sample_entity	sample_entity_single_property_indexed	10000	-1.601%	-2.163%	-1.068%

Unchanged / inconclusive (CI crosses 0%)

Group	Bench	Param	Change	CI Lower	CI Upper
large_dataset	bench_query_population_multi_unindexed_entities		1.911%	0.374%	3.433%
large_dataset	bench_filter_unindexed_entity		1.725%	-1.817%	5.125%
sampling	sampling_single_unindexed_concrete_plus_derived_entities		-1.041%	-1.249%	-0.821%
indexing	with_query_results_multiple_individually_indexed_properties_enti		-0.908%	-1.436%	-0.509%
sample_entity	sample_entity_single_property_unindexed	1000	-0.748%	-1.438%	-0.137%
sample_entity	sample_entity_single_property_unindexed	100000	0.743%	0.344%	1.140%
sample_entity	sample_entity_single_property_unindexed	10000	-0.720%	-0.931%	-0.541%
large_dataset	bench_query_population_property_entities		-0.696%	-1.357%	-0.010%
sample_entity	sample_entity_multi_property_indexed	10000	-0.673%	-1.149%	-0.318%
large_dataset	bench_query_population_multi_indexed_entities		-0.559%	-1.143%	-0.142%
indexing	query_people_indexed_multi-property_entities		-0.523%	-0.709%	-0.348%
large_dataset	bench_filter_indexed_entity		-0.505%	-2.246%	1.037%
counts	index_after_adding_entities		0.445%	-0.082%	1.009%
sampling	sampling_single_l_reservoir_entities		-0.443%	-1.450%	0.315%
large_dataset	bench_query_population_derived_property_entities		-0.423%	-0.723%	-0.118%
sampling	sampling_multiple_l_reservoir_entities		-0.390%	-0.726%	-0.069%
indexing	query_people_count_indexed_multi-property_entities		-0.368%	-1.078%	0.316%
sampling	count_and_sampling_single_unindexed_concrete_plus_derived_entiti		-0.353%	-0.517%	-0.185%
sample_entity	sample_entity_multi_property_indexed	1000	0.348%	0.129%	0.630%
algorithm_benches	algorithm_sampling_multiple_known_length		0.280%	-0.103%	0.644%
algorithm_benches	algorithm_sampling_multiple_l_reservoir		-0.275%	-0.603%	0.033%
sampling	sampling_single_unindexed_entities		0.214%	-0.072%	0.496%
large_dataset	bench_query_population_indexed_property_entities		0.190%	-0.096%	0.518%
sampling	sampling_multiple_known_length_entities		0.188%	-0.090%	0.490%
algorithm_benches	algorithm_sampling_single_rand_reservoir		-0.172%	-0.435%	0.018%
counts	single_property_indexed_entities		-0.168%	-0.609%	0.313%
indexing	with_query_results_single_indexed_property_entities		-0.157%	-0.886%	0.645%
large_dataset	bench_match_entity		-0.146%	-0.533%	0.194%
sample_entity	sample_entity_multi_property_indexed	100000	0.140%	-0.363%	0.700%
algorithm_benches	algorithm_sampling_single_l_reservoir		-0.134%	-0.287%	0.002%
counts	single_property_unindexed_entities		-0.099%	-0.595%	0.423%
algorithm_benches	algorithm_sampling_single_known_length		-0.095%	-0.279%	0.072%
indexing	with_query_results_indexed_multi-property_entities		0.091%	-0.084%	0.260%

Not Compared (no baseline yet)

Group	Bench	Reason
(none)